Conversions were not that uncommon, and often not just simple ones like converting 2-8-0s into 0-8-0 switchers, which was very common 100+ years back.
For example, Great Northern found their P-1 class 4-8-2 engines were too slow for passenger service, so they converted them to Q-2 class 2-10-2 freight engines. GN also converted their M-2 2-6-8-0 Mallets into O-7 class 2-8-2s; many were later converted into the O-8 class.
